Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored, for example because they can use a wider variety of inks.
Piezoelectric ink jet print heads typically include a flexible diaphragm and an array of piezoelectric elements (i.e., transducers or actuators) attached to the diaphragm. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric element bends or deflects causing the diaphragm to flex which expels a quantity of ink from an ink chamber through a nozzle. The flexing further draws ink into the ink chamber from a main ink reservoir through an opening to replace the expelled ink.
Increasing the printing resolution of an ink jet printer employing piezoelectric ink jet technology is a goal of design engineers. One way to increase the resolution is to increase the density of the piezoelectric elements. To attach an array of piezoelectric elements to pads or electrodes of a flexible printed circuit (flex circuit) or to a printed circuit board (PCB), a quantity (i.e., a microdrop) of conductor such as conductive epoxy, conductive paste, or another conductive material is dispensed individually on the top of each piezoelectric element. Electrodes of the flex circuit or PCB are placed in contact with each microdrop to facilitate electrical communication between each piezoelectric element and the electrodes of the flex circuit or PCB.
A flex circuit having an array of bumped (i.e., embossed) contact pads can also be attached to a piezoelectric array. The flex circuit can include an array of bumped contact pads, where each bumped pad is electrically coupled to a piezoelectric element using, for example, a conductor such as solder or conductive epoxy. Flex circuits including an array of bumped pads are discussed in U.S. Ser. No. 12/795,605, filed Jun. 7, 2010, and U.S. Ser. No. 13/232,465, filed Sep. 14, 2011, each of which is incorporated herein by reference in its entirety.
Embossing a flex circuit can be performed using a die set which includes a post plate having a plurality of posts that are square or rectangular in cross section and a die having a plurality of openings. The flex circuit with a plurality of unbumped contact pads is placed between the post plate and the die. The plurality of contact pads on the flex circuit is aligned with the posts and die openings, and pressure is applied between the post plate and die such that the contact pads are forced into the openings by the posts. Because the contact pads are metal they maintain their deformed shape to provide a plurality of embossed contact pads of a bumped flex circuit.
As resolution and density of the print heads increase, the area available to provide electrical interconnects decreases. Routing of other functions within the head, such as ink feed structures, compete for this reduced space and place restrictions on the types of materials used. Methods for manufacturing a print head having closely space electrical contacts that can be manufactured with increased yields and improved reliability would be desirable.